A phased array antenna uses multiple radiating elements to transmit, receive, or transmit and receive radio frequency (RF) signals. Phase shifters are used in a phased array antenna in order to steer the beam of the signals by controlling the respective phases of the RF signals communicated through the phase shifters. Phased array antennas are used in various capacities, including communications on the move (COTM) antennas, satellite communication (SATCOM) airborne terminals, SATCOM mobile communications, and SATCOM earth terminals. The application of mobile terminals typically requires the use of automatic tracking antennas that are able to steer the beam in azimuth, elevation, and polarization to follow the satellite's position while the terminal is in motion. Moreover, a phased array antenna is typically desired to be “low-profile”, small and lightweight, thereby fulfilling the stringent aerodynamic and mass constraints encountered in the typical mounting.
One well known type of phased array antenna is an electronically steerable phased array antenna. The electronically steerable phased array antenna has full electronic steering capability and is more compact and lower profile than a comparable mechanically steered antenna. The main drawback of fully electronic steering is that the antenna usually requires the integration of numerous expensive analog RF electronic components which may prohibitively raise the cost for commercial applications.
In a typical prior art embodiment, a phased array antenna comprises a radiating element that communicates dual linear signals to a hybrid coupler with either a 90° or a 180° phase shift and then through low noise amplifiers (LNA). Furthermore, the dual linear signals are adjusted by phase shifters before passing through a power combiner.
In the prior art, a typical digital phase shifter uses a switched delay line that is physically large and operates over a narrow band of frequencies due to its distributed nature. Another typical digital phase shifter implements a switched high-pass low-pass filter architecture, which has better operating bandwidth compared to a switched delay line but is still physically large. Also, the phase shifter is often made on gallium arsenide (GaAs). Though other materials may be used, GaAs is a higher quality material designed and controlled to provide good performance of electronic devices. However, in addition to being a higher quality material than other possible materials, GaAs is also more expensive and more difficult to manufacture. The typical phased array components take up a lot of area on the GaAs, resulting in higher costs. Furthermore, a standard phase shifter has high RF power loss, which is typically about n+1 dB of loss, where n is the number of phase bits in the phase shifter. Another prior art embodiment uses RF MEMS switches and has lower power loss but still consumes similar space and is generally incompatible with monolithic solutions. Furthermore, the typical components in a phased array antenna are distributed components that are frequency sensitive and designed for specific frequency bands.
Quadrature hybrids or other differential phase generating hybrids are used in a variety of RF applications, including phased array antennas. For example, quadrature hybrids are used for generating circular polarization signals, power combining, or power splitting. Generally, the outputs of a quadrature hybrid have equal amplitude and a 90° phase difference. The quadrature hybrid is often implemented as a distributed structure, such as a Lange coupler, a branchline coupler, or a ring hybrid. Other RF hybrids, such as a magic tee or a ring hybrid, result in 180° phase shift. In general, an RF hybrid uses distributed components, limited in frequency band and requires significant physical space inversely proportional to an operating frequency. Moreover, the quadrature hybrid is typically made of GaAs and has associated RF power loss on the order of 3-4 dB per hybrid when used as a power splitter.
An in-phase hybrid may be configured as a power combiner or power splitter in a variety of RF applications, including phased array antennas. In an exemplary embodiment, the outputs of an in-phase hybrid have equal amplitude and a substantially zero differential phase difference. In another exemplary embodiment, the inputs of an in-phase hybrid configured as a power combiner encounter substantially zero differential phase and amplitude summation of the two input signals. In a typical embodiment of a power combiner, the in-phase hybrid is implemented as a distributed structure such as a Wilkinson hybrid. In general, an in-phase hybrid is limited in frequency band and requires significant physical space that is inversely proportional to the operating frequency. Like the quadrature hybrid, the in-phase hybrid is typically made on GaAs. Moreover, the in-phase hybrid generally has associated RF power loss on the order of 3-4 dB per hybrid when used as a power splitter and an associated RF power loss of about 1 dB when used as a power combiner.
Thus, a need exists for a phased array antenna architecture that is not frequency limited or polarization specific. Furthermore, the antenna architecture should be able to be manufactured on a variety of materials and with little or no associated RF power loss. Also, a need exists for a phased array antenna that uses less space than a similar capability prior art architecture, and is suitable for a monolithic implementation.